FIELD OF THE INVENTION
Many devices are on the market which utilize rechargeable direct current battery packs as an energy source. Cameras, tape recorders, hand tools, shavers and a myriad of other appliances are typical examples. To accomplish recharging, an AC to DC converter is often employed to convert household alternative current line voltage to a DC voltage in the range of from 3 to 10 volts. Where the portable appliance is of the type having a removable power pack, it is convenient to have a charging station powered by the converter which accepts the battery pack and which further incorporates means for providing a visual indication of the condition of the battery pack being tested or charged. Also, because users of the foregoing types of appliances may not have a particular skill in the electronics field, it is desirable that the combination test stand and recharging station be substantially fool-proof in its operation. Furthermore, because of the economic choice between non-rechargeable and rechargeable power packs, it is essential that the apparatus utilized to provide the recharging and testing be low in cost so that the rechargeable power pack can remain economically competitive.
It is known in the prior art to provide charging devices for rechargeable batteries wherein a visual indication is given that charging current is flowing to the rechargeable battery. For example, the Dobie Pat. No. 3,746,961 discloses an AC to DC converter in which a neon lamp is provided which glows so long as charging current is flowing through the battery. However, when the battery becomes fully charged, the neon bulb ceases to carry a sufficient potential across it to continue glowing. The circuit of the Dobie patent, however, suffers from the defect that the lack of a visual indication is not necessarily indicative that the rechargeable battery has been fully charged. The neon glow tube will also be extinguished in the event of an open circuit between the battery to be charged and its contacts with the AC to DC converter.
Similarly, the Bogut U.S. Pat. No. 4,006,396 discloses a battery charging apparatus in which light emitting diodes are used to provide a visual indication that charging current is being supplied to the battery. However, in the Bogut patent there is no provision for indicating the charge status of a battery, i.e., whether it is in partially discharged condition or fully charged. Furthermore, the circuitry employed in the charging apparatus of the Bogut patent is relatively complex and therefore costly. As such, the arrangement may not be practical from the standpoint of marketability in that consumers might find it more economical to use throw away batteries rather than incurring the cost of the charging unit.